FIG. 1 shows a power-saving scheme according to IEEE Standard 802.11-2012, the entire disclosure of which is incorporated herein by reference. In FIG. 1, three stations A, B, and C form an independent basic service set (IBSS), also known as ad hoc mode. Each of the stations alternates between a doze (or, sleep) state, in which data is not transmitted or received, and an awake state, in which data can be transmitted and received. Each of the stations is required to wake up just before each beacon, three of which are shown at 104-1, 104-2, and 104-3 (collectively, “beacons 104”).
After waking up for the beacon, each station remains awake for a period of time called an announcement traffic indication message (ATIM) window. During the ATIM window, each station determines whether buffered frames can be sent to other stations and whether to expect to receive frames buffered at other stations.
For example, see the ATIM window following beacon 104-2 of FIG. 1. Station A transmits an ATIM frame 108 to station B, which is shown receiving the ATIM frame at 112. Station B acknowledges that station B will wait to receive data from station A by transmitting an acknowledgment 116, shown being received by station A at 120.
Because station A has identified an available recipient for a buffered frame, and because station B expects to receive a frame from a sender, stations A and B will remain in the awake state after the ATIM window and not return to the doze state. By contrast, station C, which does not have frames to transmit to stations A or B, and has not been notified of any queued frames at station A or station B, returns to the doze state after the ATIM window.
As prearranged, after the ATIM window, station A transmits a data frame 124 to station B, which is shown being received at 128. Station B signals a successful transmission by transmitting an acknowledgement 132 to station A, shown being received at 136. Stations A and B then remain awake for the remainder of the beacon interval—i.e., the time until the next beacon 104-3. Stations A and B, along with station C, are all awake for the ATIM window following beacon 104-3. This approach allows stations to doze for a significant portion of each beacon interval, and only remain awake when data transfer has been prearranged.
The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.